1. Field of the Invention
This invention relates to computer-aided machining systems. In particular, this invention relates to a computer-aided machining system and method for implementing the geometric intersection of offset surfaces and drive surfaces to automatically generate tool paths.
2. Description of the Prior Art
The use of computers in machining or manufacturing of three-dimensional components is well known. In such systems, it is necessary to calculate a cutting path for a machine tool based upon the geometry of both the cutting tool and the component to be manufactured. At present the leading system frequently employed in such operations is the automatically programmed tool system (or "APT"). This system enjoys widespread use and has a broad range of capabilities. The APT system derives a control point curve for the tool from the tool to machine the component using a recursive procedure. Recursion is stopped when the tool is within a tolerance band. As a result the APT system is not an exact one, but relies upon the tool moving within a desired tolerance to control the machining operation. Because the APT system requires the computation of tool passes one at a time with the user overseeing the tool passes, it is undesirably slow.
In operation, the APT system attempts to convert all surfaces of the component into a single surface, and is therefore limited to a fixed number of surfaces for simultaneous cutting. For example, if an automobile part such as a door frame with 200 separate surfaces is being machined, the APT system requires the door to be broken into different portions with each portion machined separately from the other portions. As a result, writing the program to control the appropriate machine tools for the machining of the door is extremely complex.
An additional disadvantage of the APT system is its inability to handle tangent discontinuities, that is, regions on a surface such as sharp corners where a tangent to the surface changes noncontinuously. The APT system requires a smooth control point curve for its tools. Because of the recursive procedures employed in the APT system, exact solutions are not provided, and the user is required to program each pass with an understanding of the prior passes. This requires extensive operator intervention during the time the program is being created to control the machining.